1. Field of the Invention
The present invention relates a method for charging a rechargeable battery.
2. Description of the Related Art
The following Patent Document (see Japanese Laid-Open Patent Publication TOKUKAI No. HEI 8-205418) discloses a charger which charges a lithium-ion rechargeable battery. As shown in FIGS. 4 and 5 of this Document, this type of charger includes a power supply portion 1, a charge control switch 2 which is provided on a charge path, and a calculation circuit 3 (microcomputer) which detects battery voltage and charge current, and controls the power supply portion 1 and the charge control switch 2. This power supply portion 1 includes feedback circuits for current and voltage. The power supply portion 1 includes a rectifying circuit 8, a switching portion 9, a conversion transformer 11, a pulse width modulation (PWM) control circuit 13, and a photocoupler 17. The rectifying circuit 8 converts alternating current into direct current. The switching portion 9 converts the direct current of the rectifying circuit 8 into pulse current of high frequency. The PWM control circuit 13 controls the switching portion 9 and thus controls DC output. The photcoupler 17 provides a control signal to the PWM control circuit 13.
A constant current charge circuit 6 and the photocoupler 17 are used as the feedback circuit for current. When charge current exceeds a predetermined value, the photocoupler 17 is brought in a non-conduction state. In this case, based on this non-conduction state as a feedback signal, the PWM control circuit 13 controls a transistor 10 so that the output becomes low. Thus, the charge current for battery is reduced. As a result, the constant current charge circuit 6 prevents that charge current for battery becomes larger than a predetermined value I1, and charges a battery at constant current.
On the other hand, a constant voltage charge circuit 5 and the photocoupler 17 are used as the feedback circuit for voltage. When charge voltage exceeds a predetermined value, the photocoupler 17 is brought in a non-conduction state. In this case, based on this non-conduction state as a feedback signal, the PWM control circuit 13 controls a transistor 10 so that the output becomes low. Thus, the charge voltage for battery is reduced. As a result, the constant voltage charge circuit 5 prevents that battery voltage becomes larger than a predetermined value, and charges the battery at constant voltage.
Instead of this control method, the following control method has been also used. In the Document, positive and negative terminals of a differential amplifier 5A of the constant voltage charge current 5 in FIG. 5 are inversely connected, while plus and minus terminals of a differential amplifier 6A of the constant current charge current 6 are inversely connected. In this method, the PWM control circuit 13 can be controlled so that, when charge voltage or current exceeds the predetermined value, the photocoupler 17 is brought in a conduction state. In this case, based on this non-conduction state as a feedback signal, the PWM control circuit 13 controls a transistor 10 so that the output becomes low. Thus, the charge voltage or current for battery is reduced. See Japanese Laid-Open Patent Publication TOKUKAI No. HEI 8-205418.